In Professor Masson's edition of De Quincey, Vol. VII, p. 8, is the
following discussion of the author's original sources:

"A word or two on De Quincey's authorities for his splendid sketch
called _The Revolt of the Tartars_:--One authority was a famous
Chinese state-paper purporting to have been composed by the Chinese
Emperor, Kien Long himself (1735--1796), of which a French
translation, with the title _Monument de la Transmigration des
Tourgouths des Bords de la Mer Caspienne dans l'Empire de la Chine_,
had been published in 1776 by the French Jesuit missionaries of Pekin,
in the first volume of their great collection of _Mémoires concernant
les Chinois_. The account there given of so remarkable an event of
recent Asiatic history as the migration from Russia to China of a
whole population of Tartars had so much interested Gibbon that he
refers to it in that chapter of his great work in which he describes
the ancient Scythians. De Quincey had fastened on the same document as
supplying him with an admirable theme for literary treatment.
Explaining this some time ago, while editing his _Revolt of the
Tartars_ for a set of Selections from his Writings, I had to add that
there was much in the paper which he could not have derived from that
original, and that, therefore, unless he invented a great deal, he
must have had other authorities at hand. I failed at the time to
discover what these other authorities were,--De Quincey having had a
habit of secretiveness in such matters; but since then an incidental
reference of his own, in his _Homer and the Homeridæ_,[11] has given
me the clue. The author from whom he chiefly drew such of his
materials as were not supplied by the French edition of Kien Long's
narrative, was, it appears from that reference, the German traveller,
Benjamin Bergmann, whose _Nomadische Streifereien unter den Kalmüken
in den Jahren 1802 und 1803_ came forth from a Riga press, in four